Nonlinear optics involves the interactions of electromagnetic fields in various materials which cause new fields of modified phase, frequency, amplitude or other propagation characteristics to be produced. In the area of microelectronics (optical switches, integrated circuits, frequency doubling or trebling) and communications technology, there is great interest in finding materials in which these effects occur.
Whereas, inorganic crystals, such as lithium niobate and gallium arsenide, or organic crystals, such as urea, have received attention in the past, polymeric materials having a donor/acceptor-substituted, delocalized .pi.-electron system are preferred today. In addition to the easier processibility of polymeric materials, an essential advantage is the possibility of obtaining thin, transparent films. In these films, compounds containing donor/acceptor groups are admixed with a polymer matrix or bonded to a polymer backbone and can be aligned by means of electrical or magnetic fields.
In addition, it may be advantageous if such polymers, in addition to nonlinear optical properties, also have liquid-crystalline properties. In this respect, reference is made, for example, to EP 262,680 A (published on Apr. 6 1988), U.S. Pat. No. 4,810,338 (published on Mar. 7, 1989), EP 271,730 A (published on Jun. 22, 1988), U.S. Pat. No. 4,779,961 (published on Jul. 5, 1988) from Hoeschst Celanese Co. In these publications, liquid-crystalline polymers having nonlinear optical properties are described. However, high-molecular-weight polymers can usually only be oriented by applying a strong electrical or magnetic field.
It is therefore an object of the present invention to provide compounds which have nonlinear optical properties and can readily be oriented in a simple manner, even without application of electrical or magnetic fields. A further object of the present invention is to provide compounds of the abovementioned type which additionally have liquid-crystalline properties.